This invention relates to a mechanical pressing machine of the type in which a slider is reciprocally moved linearly relative to a frame through a plate cam.
In a mechanical pressing machine employing a plate cam, the plate cam is fixedly mounted on an input shaft to which power is transmitted from a motor through a flywheel, and a pair of upper and lower cam followers are mounted on a slider which is mounted on a frame for sliding movement in a vertical direction. A peripheral edge of the plate cam is held between the pair of cam followers, and with this arrangement a rotational motion of the plate cam is converted into a reciprocal linear motion of the slider. When imparting the reciprocal motion to the slider, an inertia load of the slider, an unbalanced load, a pressing load and so on give fluctuating load torques to the input shaft. When these fluctuating load torques increase, the input shaft may fail to rotate only by the drive torque of the motor. To avoid this, a flywheel has heretofore been attached to one end of the input shaft so that an abruptly-fluctuating load torque of the input shaft can be absorbed by an inertia force of the flywheel. With this arrangement, the maximum value of the input torque is alleviated, and therefore the machine can be operated by an output torque of the relatively small motor.
Recently, because of an increasing demand for a small-size, high-density design of electronic components and also for a clean environment, it has been desired to provide a high-performance mechanical pressing machine less noisy and highly precise. Reviewing pressing machines from this point of view, it will be appreciated that the currently-available mechanical pressing machines are so designed as to absorb all of the fluctuating loads by means of a flywheel. It is very rational and most desirable from the viewpoint of a mechanism to absorb an excessively large load fluctuation, produced instantaneously as in a pressing operation, by the inertia force of a large flywheel; however, although a constant load fluctuation, produced when imparting a reciprocal motion to the slider, can be ignored during a low-speed operation, its energy exceeds the energy of the pressing operation during a high-speed operation, so that the speed of rotation of the input shaft attached to the flywheel increases and decreases, and hence varies periodically for every revolution. It is known that such variations in rotation of the input drive system cause vibrations of the press and noises, and also adversely affect the durability of a clutch and a brake.